A common approach for laying pipe employs a diesel powered tracked vehicle having a side boom for positioning the pipe in or on the ground. With the boom positioned on one side of the tractor, a counterweight is typically provided on the opposing side of the tractor to compensate for the weight of the pipe. The tractor typically includes a closed, pressurized hydraulic system for pipelayer control. The tractor travels generally parallel with the pipeline, with its offset position from the pipeline changing with conditions such as a terrain, obstacles, etc. The position of the counterweight is adjusted in accordance with the weight of the pipe and the inclination of the boom. Prior approaches have met with only limited success in this area. In addition, with the increasing size of pipelaying structures to accommodate larger and heavier pipes, the capacity of the load and boom motors has correspondingly increased. As a result, retraction of the boom to the full-up position by a high powered winch system frequently results in damage to the boom as well as to its mounting hardware. Finally, current pipelayers raise the load either mechanically or hydraulically and lower the load by mechanically or hydraulically braking either the load or boom winch or by means of a counterbalance valve. If the brake is not properly adjusted in retarding winch rotation, the operator can lose the load resulting in a dangerous situation and possibly damage to the pipe.
The present invention addresses the aforementioned limitations of the prior art by providing a tractor mounted hydraulic pipelayer with a side boom which prevents over-rotation of the boom, applies positive drive to both the boom and load winches during lifting and lowering, and orients and positions the counterweight to provide a high degree of tractor stability and a high level of safety.